Formation of Concentration Gradient
Single Line Configuration
2.2.5.
The Lab-on-valve module comprises a flow cell, monitored by optical fibers, a flow through sample port used in this experiment to inject a blue dye (bromothymol blue), a diluent port used to inject a colorless diluent and a central port communicating with a pump via a holding coil.
The clip shows the aspiration of 100 microliters of a dye into the holding coil, followed by aspiration of 50 microliters od diluent from diluent port. Next valve turns and the flow is reversed, transporting the dispersed sample zone into and trough the flow cell.. Finally the flow rate is accelerated to purge the flow channel and flow cell. Note that the leading section of dye enters the flow cell almost undiluted. Observe the shape of the concentration gradient, easily seen as the tailing section of the dye zone passes trough the flow cell. The result is that the gradient comprises a very wide range of concentration starting with undiluted dye (D=1).
This experiment is repeated in the next page, using a reagent to visualize mixing and ensuing chemical reaction.
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